kernel: Use fs:: namespace and unicode path in kernel tests

Add support for unicode characters in paths to the kernel tests by using
our fs:: wrappers for std::filesystem calls and adding the windows
application manifest to the binary. This exercises their handling
through the kernel API.

test/lint/test_runner/src/lint_cpp.rs

@@ -105,7 +105,6 @@ pub fn lint_std_filesystem() -> LintResult {
             "./src/",
             ":(exclude)src/ipc/libmultiprocess/",
             ":(exclude)src/util/fs.h",
-            ":(exclude)src/test/kernel/test_kernel.cpp",
             ":(exclude)src/bitcoin-chainstate.cpp",
         ])
         .status()